1. Field of the Invention
The present invention relates to a wireless measuring device to collect measured data obtained by measuring a physical quantity of a temperature or the like at a plurality of places.
2. Description of the Related Art
In the case where a characteristic of a temperature or the like is measured at many places reaching several tens of places or more and profiling of the measured result is performed, if a cable is used for receiving and transmitting a measuring signal, there are some cases in which wiring work of the cable requires much time and labor depending on some subjects to be measured and/or on some environments in which a measuring device is installed and the wiring work itself is made difficult. For example, in a thermal vacuum test for an artificial satellite, temperatures must be measured at 500 to 1000 places and a period of one month or more is required only for wiring work in some cases. Technology generally called a “telemetering (wireless measurement)” method is known (disclosed in, for example, Japanese Patent Application Laid-open No. 2004-13572) in which receiving and transmitting of data obtained by measurement at many measuring places are achieved by wireless communication.
A conventional measuring device employing the telemetering technology is classified roughly into two types. One is a device whose child unit has a function of receiving and transmitting signals and another is a device whose child unit has a function of only transmitting signals. The child unit of the former is in a receiving state all the time with the aim of receiving a measurement instructing signal from a parent unit. Therefore, a small-sized child unit using a battery, due to rapid consumption of the battery, is unsuitable for long time or long period measurement. The latter transmits measured data using a timer embedded in its child unit as a reference for measurement. In this case, errors always occur in the timer which causes transmitting timing to coincide among child units and a collision to occur among pieces of measured data, thus inducing a fear of failing to capture measured data.